Commitments and Contingencies (Commitments) (Details) (USD $)				6 Months Ended				1 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Indemnities under International Asset Sale Agreements	Jun. 30, 2012 Minimum	Jun. 30, 2012 Maximum	Jun. 30, 2012 Coal transportation agreements	Jun. 30, 2012 Homer City	Feb. 20, 2003 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement	Jun. 30, 2012 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement cases	Jun. 30, 2012 Edison Mission Marketing and Trading, Inc	Jun. 30, 2012 Homer City plant Senior Rent Reserve Letter of Credit	Jun. 30, 2012 Senior Secured Bonds due 2019 Homer City	Jun. 30, 2012 Senior Secured Bonds due 2026 Homer City
Homer City Lease and Environmental Project
Letter of credit											$ 48,000,000
Estimated capital costs for SO2 reduction technology				700,000,000	750,000,000
Stated interest rate (as a percentage)												8.137%	8.734%
Assets	8,254,000,000	8,323,000,000					181,000,000
Liabilities	6,592,000,000	6,659,000,000					97,000,000
Intercompany accounts receivable due from Homer City										37,000,000
Coal Transportion Commitments
Coal transportation agreements, aggregate						2,400,000,000
Coal transportation agreements, remainder of 2012						229,000,000
Coal transportation agreements, 2013						292,000,000
Coal transportation agreements, 2014						287,000,000
Coal transportation agreements, 2015						261,000,000
Coal transportation agreements, 2016						261,000,000
Coal transportation agreements, thereafter						1,100,000,000
Guarantees and Indemnities
Percentage reimbursement obligation for asbestos claims (as a percent)								50.00%
Term of asbestos supplemental agreement (in years)								5 years
Term of asbestos supplemental agreement, automatic renewal period (in years)								1 year
Number of cases not settled and dismissed creating potential liability (in cases)									218
Liability under indemnities			$ 27,000,000						$ 53,000,000